The present invention relates to an input-output integrated type display device, which is able to obtain an input position by detecting position information inputted with a pen and to output an image in this obtained position.
Conventionally, a tablet integrated type liquid crystal display, in which a transparent tablet and a liquid crystal display are integrated with each other, has widely been used as an input-output integrated type display device as described above. There are various types of this tablet integrated type liquid crystal display, and a resistance system used for a tablet is most widely adopted.
As the aforementioned conventional tablet integrated type liquid crystal display, there is one formed by sticking a transparent tablet provided independently of a liquid crystal display on the front side of this liquid crystal display to each other. In the case of this structure, the transparent tablet is independently provided on the front side of the liquid crystal display. Therefore, due to the existence of the transparent tablet, there are the problems of a reduction in transmittance of light from the liquid crystal display, an increase in parallax between an input position with a pen and a display position, an increase in cost, an increase in module thickness and module area and so on.
Accordingly, there has been proposed a structure such that an input-output integrated type display device is constructed solely of a display panel by providing the liquid crystal display itself with an input position detection function. For example, Japanese Patent Laid-Open Publication No. HEI 6-314165 discloses a display integrated type tablet device such that a TFT substrate on which row electrodes, column electrodes, TFT's (Thin Film Transistors) and pixel electrodes are formed and an opposite substrate on which opposite electrodes are formed are laminated with each other with interposition of a liquid crystal layer, row electrodes are scanned by inputting a row electrode scanning pulse sequentially to the row electrodes in a display period, column electrodes are scanned by inputting a column electrode scanning pulse sequentially to the column electrodes in a non-display period, the input position is detected on the basis of a voltage induced at the tip electrode of a detection pen due to this scanning, and the input position is displayed in the position. In the case of this display integrated type tablet device, by placing the TFT substrate on the front side, placing the opposite substrate on the rear side and applying light with back light from behind the opposite substrate, high-frequency noises from the back light are interrupted by the opposite electrode, preventing noises from being superimposed on an induced voltage induced at the detection pen.
Moreover, Japanese Patent Laid-Open Publication No. HEI 8-146381 discloses an active matrix type liquid crystal display integrated type tablet. In this official gazette, a rod-shaped metal electrode is arranged on the four sides of the opposite electrode of the active matrix type liquid crystal display (TFT-LCD), and a DC voltage is supplied from each metal electrode to the opposite electrode in a period of operation of writing into the liquid crystal display, making the opposite electrode have same potential. On the other hand, a tablet operation period is time-sharingly divided into a longitudinal detection period and a transversal detection period. In the longitudinal detection period, an AC signal is applied to one of two metal electrodes located at both ends in the longitudinal direction of the opposite electrode, and a voltage of 0 V is applied to the other. Then, the position in the longitudinal direction of the pen is obtained by detecting a potential at the position of the pen. Likewise, the position in the transversal direction of the pen is obtained in the transversal detection period.
However, the aforementioned conventional input-output integrated type display device has the following problems. That is, in the case of the display integrated type tablet device disclosed in Japanese Patent Laid-Open Publication No. HEI 6-314165, which is required to scan both the row electrodes and the column electrodes at the time of input position detection, consumes considerable time for the detection of the input position. Furthermore, since the row electrode scanning is performed in the display period, it is impossible to detect the input position two or more times in one frame period. Moreover, it is required to obtain the position of the detection pen by analyzing the time series of the voltage induced at the detection pen due to the scanning in a shaping manner, and the detection accuracy of the detection pen position is poor. Moreover, there is a problem that the circuit construction becomes complicated in order to perform the scanning.
Furthermore, light such as extraneous light incident from the front side is reflected on the row electrodes and the column electrodes formed on the TFT substrate. Accordingly, there is another problem that contrast is reduced in the portion where the extraneous light exists. Moreover, when the display integrated type tablet device of the aforementioned construction is employed as a reflection type, it is required to provide a reflecting plate, which is normally formed on the TFT substrate concurrently serving as a pixel electrode, on the opposite substrate side where a color filter is formed, and this leads to a problem that the reflection area cannot be secured broad.
On the other hand, in the case of the active matrix type liquid crystal display integrated type tablet disclosed in Japanese Patent Laid-Open Publication No. HEI 8-146381, it is required to arrange a metal electrode on the four sides of the opposite electrode, make the voltage application to the metal electrode in the writing operation period differ from that of the tablet operation period and further change the direction of voltage application with time-sharingly dividing the tablet operation period into the longitudinal detection period and the transversal detection period. This leads to a problem that the mounting form of the peripheral circuit, which controls the voltage application to the opposite electrode, becomes complicated, possibly causing cost increase and module form change. Furthermore, spreading resistance exists in the opposite electrode. Accordingly, there is a problem that the input position detection accuracy is disadvantageously lowered due to the spreading resistance.